Tantalum carbide lamp



March 2, 1937. M ANDREWS- 2,072,788

'I ANTALUM CARBIDE LAMP Filed June 15, 1935 Inventor- R. Andrews, Decd,

1 I by Mary Andr'ewS Westendor-p, Her Executrix,

Her- Atigorneg.

- 35 able for use with the invention, while Figs. 2

Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE TANTALUM caaama LAMP Application June 15,

Claims.

The present invention relates to incandescent lamps. and more particularly to lamps having filaments which consist, in whole or in part, of a highly refractory carbide, such, for example,

5 as the carbide of tantalum.

It has been found that the carbides of tantalum and the allied metals are capable of resisting extremely high temperatures, even exceeding those permissible with tungsten. For this reason they are eminently fitted for the construction of incandescible filaments to be used in the production of high intensity white light. A limitation upon their use for this purpose is imposed, however, by the fact that chemical dissociation of the carbide takes place during lamp operation which tends seriously to shorten its effective life.

The invention contemplates providing a source of uncombined carbon adjacent the carbide filament and enveloping the same in a medium zocapable of transferring carbon from the source to the filament. For an enveloping medium there may be used a volatile carbon-bearing substance such as carbon di-sulphide which is decomposible at temperatures above 1000 C., but

is capable of being regenerated in the presence of carbon at temperatures below that value.

The novel features which are considered to be characteristic of the invention will be pointed out with particularity in the appended claims.

The invention itself will be best understood by reference to the following specification taken in connection with the appended drawing, in which Fig. 1 is a perspective view of a lamp embodying the invention which is considered suitand 3 illustrate modifications of which the invention is capable.

Referring more particularly to Fig. 1, there is illustrated a transparent bulbous container l pro- 4 vided with an reentrant stem. 2 and a press 3;

Enclosed by-the container and centrally disposed therein is mounted an incandescible filament 4. Heating current for the filament is supplied through a pair of lead-in wires 5 and 6 which are suitably sealed into the press 8. To prevent excessive thermal evaporation of the filament material the envelope I may be filled at the time of seal-oil with a quantity of argon gas at a pressure within a range of about V to 2 atmospheres.

The filament 4 may consist wholly or partly of a carbide of the group of metals including tantalum, hafnium, zirconium and niobium, or a mixture of two or more such carbides. Particular compositions suitable for the purposes of 1935, Serial No. 26,820

the invention include the following (1) a mixture of four parts tantalum carbide and one part hafnium carbide; (2) a mixture of-four parts tantalum carbide and one part zirconium carbide. r

The filament may be formed by any of the many methods known to the prior art. A procedure which has been found expedient includes mixing the oxide of tantalum or a corresponding metal with a cellulose 'blnder to obtain a plastic mass. The mixture is then extruded through a fine orifice and the resulting filament carbidized by heating in a reduction atmosphere in contact with free carbon.

Incandescible filaments prepared in this way and enveloped in an inert atmosphere may be heated by passage of electric current to temperatures at least as high as 3000 C. without serious thermal deterioration. Under such conditions the filament will act as an incandescent source of white light characterized by an efiiciency even exceeding that of the commercial tungsten lamp.

For preventing chemical dissociation of the carbide during lamp operation there may be used a body of uncombined carbon. In Fig. 1 this is illustrated as a deposit of lamp-black or soot collected on the lead-in wires 5 and 6 and the press and stem of the container I. To facilitate the transfer of carbon from this source of supply to the carbide filament there is provided in the container I a quantity of a regenerative or vaporizable carbonaceous medium. By a regenerative carbonaceous medium I intend to designate a medium which is capable of decomposing into free carbon and a volatile component at the operating temperature of the filament 4, such component being further capable ofreacting with the uncombined carbon at the lower temperature prevailing in its vicinity to cause regeneration of the medium. A particular example of such a medium comprises carbon disulphide.

As a result of the decomposition of the carbon disulphide coming into contact with the incandescent carbide surface a continuous deposit of carbon will occur on the body of the filament, and tend to prevent its decarbidization. The liberated atomic sulphur, on the other hand. will volatilize into contact with the uncombined carbon in the cooler regions of the container, thus regenerating carbon disulphide and making possible a continuation of the cycle. The temperature of the lead-in wires and associated parts will be high enough during normal lamp operation to favor the formation of the disulphide.

On the other hand the much higher tempera- While particular embodiments of the invention ture required for the dissociation process will not be present.

While reference has been made particularly to carbon disulphide as a suitable medium for use in connection with the invention, other vaporizable materials of similar characteristics may be employed in accordance with the invention. Thus, carbon tetrachloride may be cited as an instance of a chlorine compound which, while decomposible in the presence of heat to liberate free carbon, is capable oi spontaneous regeneration at lower temperatures. Atomic chlorine which will be produced by the decomposition is sufliciently active to react with uncombined carbon under the conditions stated.

A second structural embodiment which may be employed in connection with the invention is shown in Fig. 2, in which parts corresponding to those illustrated in Fig. 1 are identically numbered. In this modificationthereis provided a source of uncombined carbon a solid body of carbonaceous material 8 supported adjacent the carbide filament I by 9. depending rod 9. As a consequence of this arrangement heat radiated from the filament is able to maintain the surface of the body 8 at a sufilcient temperature to promote the ready combination of its carbon with the volatile products of decomposition of the carbonaceous medium enclosed in the container I. The spacing chosen may be such that optimum temperature conditions for the alternate decomposition and regeneration of the gas will obtain.

In the modification illustrated in Fig. 3 the source of uncombined carbon takes the form of a carbonaceous filament i2 suspended below the incandescible refractorycarbide filament ii. Depending lead-in conductors l8 and i4 suitably sealed into the press I! are adapted to supply heating current to the member l2. In this way its temperature, while being kept a predetermined number of degrees lower than that of the main filament. can be held sumciently high to expedite the regeneration of the carbon-bearing medium. Assuming the temperature of the tungsten carbide to be in the neighborhood of 3000 C. a temperature of about 800 C. will prove most advantageous for the auxiliary filament i2 if carbon disulphide is the volatile medium employed. The filament resistance may be chosen so that this temperature will result when line voltage is impressed across the lead-in conductors l3 and II. This can obviously be regulated by interspersing the carbonaceous material with a suitable high resistance binder, or by properly selecting the dimensions oi the filament.

have been shown. it will of course be understood that the invention is not limited to the precise embodiment illustrated and described since many other modifications in the structure may be made, and the appended claims are intended to cover all such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. Anelectric lamp comprising a container enclosing an incandescible filament containing tantalum carbide, a source of uncombined carbon and a quantity of carbon disulphide for supplying carbon from said source to said carbide to counteract dlssocation thereof during operation of said lamp.

2. An electric lamp comprising a container enclosing an incandescible filament containing tantalum carbide, a carbonaceous bocLv adjacent said filament and a regenerative carbonaceous gas for supplying carbon from said body to said carbide to counteract dissociation thereof .during operation of said lamp.

3. An electric lamp comprising a container enclosing a filament containing tantalum carbide, a second filament consisting essentially of uncombined carbon, separate lead-in conductors for heating said filaments, and a regenerative carbonaceous gas for supplying carbon from said second filament to the carbide of said first filament to counteract dissociation thereof during operation of said lamp.

4. An electric lamp comprising a container enclosing an incandescible element containing a carbide of the group consisting of tantalum, hafnium, zirconium and niobium, a source of uncombined carbon and a carbonaceous gas which is capable of decomposing into free carbon anda volatile component at the operating temperature of said element, said component being further capable of reacting with the uncombined carbon under the normal operating conditions of the lamp thereby to cause regeneration of said gas.

5. An electric lamp comprising a container enclosing an incandescible element containing tantalum carbide. a source of uncombined carbon and a carbonaceous gas which is decomposed into a volatile component and free carbon at the operating temperature of said element, said component being further capable of reacting with the uncombined carbon underthe normal conditions of operation of the lamp thereby to cause regeneration of saidgas.

' MARY ANDREWS WESTENDORP. Ezecutria: of the Estate of Mary R Andrews,

Deceased. I 

